1. Field of the Invention
The present invention relates to a hydraulic continuously variable transmission. More particularly, the present invention relates to a hydraulic continuously variable transmission including a swash plate plunger pump and a swash plate plunger motor connected to each other through a closed hydraulic circuit, and particularly to a hydraulic continuously variable transmission including a swash plate servo device for pivotally adjusting a swash plate member of a swash plate plunger motor.
2. Description of the Background Art
As to hydraulic continuously variable transmissions including a hydraulic pump and a hydraulic motor in combination, a variety of forms of configurations have been known and put to practical use.
One example of a commercial hydraulic continuously variable transmission was sold by Honda and marketed under the trademark “Hondamatic” on the 2001 Honda Fourtrax Foreman Rubicon™ TRX500 ATV.
Another example of a known hydraulic continuously variable transmission is disclosed in Japanese Patent Laid-open No. Hei 6-2753 and Japanese Patent Publication No. Hei 7-88884 proposed by the present applicant. The hydraulic continuously variable transmission disclosed in these patent documents includes a swash plate plunger pump, a swash plate plunger motor, and a closed hydraulic circuit for connecting a discharge port and a suction port of the swash plate plunger pump to a suction port and a discharge port of the swash plate plunger motor, wherein a pump swash plate member is driven by an engine, a pump cylinder and a motor cylinder are connected to each other and disposed in a connected state on an output shaft, a motor swash plate is restricted in rotation, and the motor swash plate angle can be regulated variably.
Thus, in order to variably regulating the motor swash plate angle, hitherto, a configuration has been adopted in which an arm portion formed by projecting an outer circumferential portion portion of the motor swash plate (motor pivoting member) in a radial direction is moved in the axial direction by a swash plate servo device to thereby pivotally move the motor swash plate. Such a swash plate servo device is disclosed, for example, in Japanese Patent Laid-open No. 2001-141024. The swash plate servo device includes a screw shaft extending in parallel to the rotational axis of an output shaft and rotatably supported on the transmission housing, a nut member which is screw-engaged with the screw shaft and to which the tip end of the arm portion is connected, and a servo motor for driving the screw shaft to rotate, and the swash plate servo device is disposed on a lateral side of and in a side-by-side relationship with the hydraulic pump and motor constituting the hydraulic continuously variable transmission.
However, since the swash plate servo device is disposed on a lateral side of and in a side-by-side relationship with the hydraulic pump and motor as above-mentioned, an attachment portion of the servo motor projects to a lateral side, whereby the size of the transmission in a side direction (a direction perpendicular to the axis) is enlarged, and the transmission is enlarged in size.
Particularly, in the case of the above-mentioned hydraulic continuously variable transmission, an input gear (primary driven gear) for receiving the rotational drive force from the engine is attached to the outer circumference of a pump casing of the hydraulic pump, and the input gear projects outwards in the radial direction, resulting in the problem that the swash plate servo device is liable to project more in a side direction so as to obviate interference with the input gear.
In addition, since the servo motor composed of an electric motor is disposed in the vicinity of a lateral side of the swash plate plunger pump and motor, the electric pump is liable to be affected by any heat coming from the side of the pump and motor.
Although the known devices have some utility for their intended purposes, there is still a need to provide an improved hydraulic continuously variable transmission.
More particularly, there is a need for an improved hydraulic continuously variable transmission including a swash plate plunger pump and a swash plate plunger motor connected to each other through a closed hydraulic circuit, and particularly to a hydraulic continuously variable transmission including a swash plate servo device for pivotally adjusting a swash plate member of a swash plate plunger motor.